Osteoarthritis is a chronic debilitating disease which affects up to 1/3 of the adult population. Growing evidence suggests that genetic factors influence its development, and a better understanding of inherited chondrodysplasias will undoubtedly shed light on the processes common to all degenerative joint disease. Spondyloepiphyseal dysplasia tarda (SEDT) is a chondrodysplasia which is characterized by disproportionate short stature, X-linked inheritance, and degenerative osteoarthritis. The goals of this project are 1) to localize and isolate the gene for SEDT, 2) to identify the molecular alterations responsible for this disease, and 3) to gain insight into the biological function of the gene product. We have studied three SEDT families, including one large pedigree which includes 16 living affected males and at least 20 carrier females. DNA linkage analysis indicates that the SEDT phenotype in these families cosegregates with polymorphic markers on chromosome Xp22, a region previously defined as harboring the SEDT disease gene. To reduce the size of the candidate area, we will expand the sample size within our families, ascertain additional families, and verify locus order by physical methods. We will identify candidate genes which both map to the region and are transcribed in cartilage using expressed sequence tagged sites (ESTs) and cDNA selection techniques. Candidate genes will be prioritized for mutation analysis based on their homology to known genes. Prime candidates will be analyzed for mutations by SSCP and direct DNA sequence analysis of genomic DNA and/or cDNA from affected individuals. This research will directly benefit families with SEDT by enhancing genetic counseling and facilitating early definitive diagnosis for individuals at risk, therefore improving their clinical care. The expression pattern and function of the SEDT gene may provide clues for designing therapeutic modalities for affected individuals. Moreover, we anticipate that the molecular delineation of SEDT will have a significant impact on our understanding of basic mechanisms responsible for maintaining cartilage integrity, as well as those contributing to cartilage degeneration in osteoarthritis.